Upgraded charging methods in the wearable field

　　As the times change and technology advances, new charging methods for wearable devices have also emerged. What are they? Let's take a look!

　　According to the Washington Post, researchers at the University of California have recently developed a new technology that can convert sweat into electricity.

　　The research team has developed a new type of bio-battery that can be attached to the user like a sticker, using lactic acid secreted by the human body during exercise to generate energy. The sensors in the bio-battery can obtain electrons from lactic acid molecules to generate electric current.

　　When people exercise, tissue cells cannot get enough oxygen and lactic acid is produced. Athletes will test the lactic acid level in their blood during physical training to evaluate the level of training. Doctors also often diagnose heart disease or lung disease by testing the lactic acid content. The current method of testing lactic acid is mainly to collect blood samples and test them at different points during exercise.

　　The team used detection technology to create a bio-battery. During the test, they found that people who do not exercise often produce more electricity through sweat. Due to poor physical reserve, after a short period of exercise, the body begins to enter an anaerobic state and produces lactic acid. The current generated by the bio-battery is very weak. The maximum power that can be obtained theoretically is 70 uW/cm² per square meter of skin. In the experiment, the 2mm X 3mm electrode only generated 4uW of power, which is not enough to drive a watch for daily use. The research team said that after further improvements, the current can reach the level of driving small electronic devices.

　　Figure 1: Like a sticker, sweat generates electricity

　　In order to extend the use time of wearable devices, next-generation battery technology is gradually emerging. Due to the limitation of thinness and size, the battery capacity and endurance of wearable devices have always been the design barriers that developers have been working hard to break through. As traditional lithium polymer batteries (LPB) have gradually become insufficient, various next-generation battery technologies have emerged and become one of the focuses of wearable device developers.

　　The design trend of future wearable devices will evolve towards multi-functional integration, minimum usage time of at least one day, thinning/lightweight/miniaturization of devices, and integration with various heterogeneous materials, which will bring severe challenges to internal battery design.

　　Although the functions of wearable devices are not complex at present, their biggest design bottleneck is the limited size, so the battery capacity cannot meet the needs of long-term use; in addition, because wearable devices must be used close to the human body and are mainly "wearable", the overall appearance design and fashion sense must also be considered. In addition to the flexible appearance being the general trend, developers will also increase the proportion of soft packaging that is very different from the hard and cold materials of general electronic products. In response to the future appearance design trend of wearable devices, their internal battery design must also be adjusted accordingly.

　　It is understood that the next-generation batteries currently under development by industry and academia can be roughly divided into three categories, namely high-energy-density batteries, solid-state ultra-thin batteries and flexible batteries. Major manufacturers including Samsung, LG, Panasonic, Sekisui Chemical and others are actively engaged in development.

　　With the same volume and thickness, if next-generation batteries are used to replace lithium polymer batteries, the device usage time can be extended by 1.4 to 1.8 times. If the capacity is the same, the thickness and weight of the next-generation batteries can be reduced by about 50% to 75%. More importantly, the next-generation batteries can also affect the overall appearance design of wearable devices. Taking smart watches and bracelets as examples, although their internal battery modules are currently designed under the watch head, the flexible "watch strap battery" will be the design goal of future developers, so that the battery capacity used in the watch head can be reduced and the thickness of the watch head can be reduced.

　　One of the biggest issues with wearables is how to keep the battery life long enough without making the device too big. Ideally, the user would not need to charge the device at all.
　　What else can you do besides charging?

　　Figure 2 Inexhaustible solar energy

　　Energy harvesting is only one aspect of making wearable devices completely free of charging. Energy storage is another aspect that has a lot of room for improvement. Another way to make wearable devices last longer or even completely free of charging is to significantly reduce the energy consumption of sensors, chips and communication systems. The success of smartphones has promoted the development of low-energy, high-performance chips. The processors of wearable devices require even less computing power and energy. To address this problem, chip manufacturers including Intel are reducing some common energy losses by integrating processors, memory and communication modules into a single chip.

　　Summary: All of the above shows that humans are pushing wearable devices into an era where charging is not required, and the author firmly believes that this era will eventually come. When this era comes, consumers' experience of using wearable devices will be different from the past, so that wearable devices can be promoted to a wider range of fields.